Who is Warren Buffett's replacement?

Billionaire investor Warren Buffett's successor is already picked. The only problem is: Who is it?

The Oracle of Omaha said in February that the Berkshire Hathaway board had selected his successor, but then did not actually name the CEO-in-waiting. Buffett's announcement on Tuesday that he has a form of treatable cancer might force the conglomerate to introduce the next CEO a littler faster than previously expected.

In his annual letter to investors released in February, Buffett said the board was "enthusiastic about my successor as CEO, an individual to whom they have had a great deal of exposure and whose managerial and human qualities they admire." But little else has been said about who would replace Buffett, who has been at the helm since the 1970s.

Berkshire might take the company annual meeting on May 5 in Omaha to give that person a little more exposure.

Among the possibilities is Ajit Jain, a longtime Berkshire employee who now runs the company’s reinsurance business. Another name mentioned often is Tony Nicely, the CEO of Berkshire's GEICO unit. Others include the heads of several of the conglomerate's businesses, including Burlington Northern CEO Matthew Rose and MidAmerican Energy Holdings CEO Matthew Rose.